Railroad freight cars that are used repeatedly for a specific purpose are usually connected together, in a generally permanent fashion, by a solid drawbar assembly. Use of this type connection will, however, still enable such freight cars to be separated when needed, such as when a car requires removal from service because of needed repairs. Therefore, a somewhat more appropriate term for the type of mechanical connection effected by this drawbar assembly is "semi-permanent" or "substantially semi-permanent".
Each of these freight cars, in addition, is equipped with a brake pipe and brake cylinders that operate the brakes of each of the freight cars. In this air brake arrangement, the brake pipes are normally serially connected together between the freight cars by a gladhand connected to a flexible hose. Further, the brake pipe will supply the pressurized air that is required by the brake control system of the train to charge the reservoirs which are located on the respective cars for the general operation of the air brake equipment disposed on each freight car.
The air brake equipment on each freight car includes an auxiliary air reservoir, an emergency air reservoir and a conventional pneumatic brake control valve such as the ABDX, ABDW or similar types of control valves. These ABDX and ABDW type brake control valves are manufactured by the Westinghouse Air Brake Company (WABCO) and are quite well known in the railway brake control art.
The typical brake control valve on a railway freight car will at least include both a service portion and an emergency portion, these particular portions being located on radially opposed sides of a pipe bracket. The pipe bracket features a number of internal passageways and ports. As is well known in the art, each port in the pipe bracket connects to one of the branch pipes positioned on the freight such as those leading to the brake pipe, the brake cylinders, and the emergency and auxiliary reservoirs. It is through these ports and internal passageways of the pipe bracket that the relevant portions of the brake control valve communicate pneumatically with piping on a railway freight car.
Both the service and emergency portions of the pneumatic brake control valve operate according to principals which are well known in the railroad industry. The service portion of the brake control valve performs several functions including: (1) controlling the flow of air from the auxiliary reservoir to the brake cylinders for making a service brake application, (2) controlling the recharging of such auxiliary and emergency reservoirs from the main reservoirs located on the locomotive and which are pneumatically connected to the freight cars, (3) controlling the exhausting of air from the brake cylinders when the brakes are released and (4) reinforcing the brake application and release signals being pneumatically conveyed by the brake pipe.
The emergency portion of the brake control valve controls, among other things, (1) the recognition of the emergency brake application signal pneumatically conveyed by the brake pipe and (2) the flow of air from both the auxiliary and emergency reservoirs to the brake cylinders during an emergency brake application. The emergency portion of the control valve on each freight car also serves to propagate the emergency application signal along the train consist by rapidly venting brake pipe pressure to atmosphere.